Ink-jet ink comprising cross-linked pigment dispersion based on polyurethane dispersants

1. An ink-jet ink comprising an aqueous ink vehicle and an aqueous pigment dispersion, wherein said aqueous dispersion comprises a colorant dispersed by a polymer dispersant, wherein said polymer dispersant is subsequently cross-linked with a cross-linking agent selected from the group consisting of epoxide, carbodiimide, N-methylol, oxazoline, silane, and mixtures thereof;

wherein the polymer dispersant prior to becoming cross-linked comprises at least one compound of the general structure of Formula I:

wherein each X is independently OH, SH, COOH or NHR 4 ;

each Y is independently O, S or NR 4 ;

each W is NH, O or S;

each R 1 is independently C 1 -C 20 alkyl, C 3 -C 20 substituted alkyl, C 6 -C 40 aryl or C 9 -C 40 substituted aryl;

each unit of —W—R 2 —W— is derived from difunctional isocyanate reactants Z 1 , Z 2 and Z 3 , wherein there are at least one unit derived from Z 1 , at least one unit derived from Z 2 and at least one unit derived from Z 3 ;

each R 3 is independently C 1 -C 20 alkyl or C 3 -C 20 substituted alkyl;

each R 4 is independently —R 3 -A, H, C 1 -C 20 alkyl or C 3 -C 20 substituted alkyl;

each A is OH, SH or COOH;

n is an integer from 2 to 30;

Z 1 is a difunctional isocyanate reactant substituted with an aqueous dispersing moiety;

Z 2 is a difunctional isocyanate reactant substituted with one or more cross-linkable moieties;

Z 3 is a polyol with MW less than 3000; and

wherein cross-linking takes place between the cross-linking agent and the cross-linkable moieties in substituent R 2 pendent to the polymer backbone and the cross-linkable moieties in X terminal to the polymer chain.

2. The ink of claim 1 , wherein Z 1 is a polyol substituted with the aqueous dispersing moiety.

3. The ink of claim 2 , wherein Z 2 is a polyol substituted with one or more cross-linkable moieties.

4. The ink of claim 2 , wherein the aqueous dispersing moiety consists of one or more carboxyl groups.

5. The ink of claim 3 , wherein the cross-linkable moiety consists of one or more carboxyl groups.

6. The ink of claim 5 , wherein Y is NR 4 .

7. The ink of claim 1 , wherein X is OH.

8. The ink of claim 7 , wherein Z 1 is a polyol substituted with the aqueous dispersing moiety.

9. The ink of claim 8 , wherein Z 2 is a polyol substituted with one or more cross-linkable moieties.

10. The ink of claim 1 , wherein X is NHR 4 .

11. The ink of claim 10 , wherein Z 1 is a polyol substituted with the aqueous dispersing moiety.

12. The ink of claim 11 , wherein Z 2 is a polyol substituted with one or more cross-linkable moieties.

13. The ink of claim 1 , wherein Y is NR 4 .

14. The ink of claim 13 , wherein R 4 is —R 3 -A.

15. The ink of claim 14 , wherein each W is O.

16. The ink of claim 14 , wherein each W is NH.

17. The ink of claim 1 , wherein the mole ratio of the cross-linkable moiety to the cross-linking agent is from 15:1 to 1:1.5.

18. The ink of claim 17 , wherein the mole ratio of the cross-linkable moiety to the cross-linking agent is from 9:1 to 1:1.1.

19. The ink of claim 18 , wherein the mole ratio of the cross-linkable moiety to the cross-linking agent is from 8:1 to 1:1.